1. Field of the Invention
The present invention relates to a ceramic electronic component, and more particularly, to a structure of an external terminal electrode, which is provided in a ceramic electronic component.
2. Description of the Related Art
Recently, with a reduction in size and thickness of electronic devices such as cell phones and portable music players, the size and the thickness of a ceramic electronic component disposed in those electronic devices have also been reduced at a high pitch. While the ceramic electronic component is usually mounted on a wiring board disposed inside the electronic device, the strength of the ceramic electronic component itself tends to lower because of the reduction in size and thickness of the ceramic electronic component. This leads to a risk that the ceramic electronic component may crack when being mounted or during use. Such a point will be described in more detail below.
FIG. 16 is a plan view of a multilayer ceramic capacitor 1 as one example of known ceramic electronic components, and FIG. 17 is a sectional view of the multilayer ceramic capacitor 1 illustrated in FIG. 16. These drawings illustrate the problems which are caused due to stress applied when the multilayer ceramic capacitor 1 is being mounted or is in a mounted state.
A ceramic element body 2 included in the multilayer ceramic capacitor 1 has a first principal surface 3 and a second first principal surface 4 arranged to face each other. FIG. 16 illustrates the second principal surface 4 arranged to direct the mounting surface side where the multilayer ceramic capacitor 1 is mounted to a wiring board. As illustrated in FIG. 16, respective ends of first and second external terminal electrodes 5 and 6, which are located on the second principal surface 4 to face each other, are arranged to extend linearly.
For example, when the multilayer ceramic capacitor 1 is mounted to a wiring board (not shown), the multilayer ceramic capacitor 1 is sucked at the first principal surface 3 by a suction head (not shown) of a mounting machine and is mounted to lands on the wiring board. As illustrated in FIG. 17, however, stress is applied to the first principal surface 3 due to inertia during the mounting operation, whereby a point 7 of application of force is formed. Further, contact points of the first and second external terminal electrodes 5 and 6, which are formed at opposite ends of the multilayer ceramic capacitor 1, with the wiring board become fulcrums 8 and 9, respectively. As a result, the ends (denoted by dotted-line circles) of portions of the first and second external terminal electrodes 5 and 6, which are extended over the second principal surface 4 on the mounting surface side, become points 10 and 11 of action, respectively. Cracks tend to occur inside the ceramic element body 2, starting from the points 10 and 11 of action.
It should be noted that the stress providing the point 7 of application of force is not limited to the above-described stress applied when the multilayer ceramic capacitor 1 is mounted, and it includes stress generated, for example, upon flexing of the wiring board during use.
Such a phenomenon, i.e., cracking, is apt to occur when the principal surfaces 3 and 4 of the ceramic element body 2 are parallel to the mounting surface of the wiring board. In particular, cracking is more apt to occur as the dimension of the multilayer ceramic capacitor 1 in the direction of height thereof is reduced.
To solve the above-described problem, Japanese Unexamined Patent Application Publication No. 2001-126950, for example, proposes an arrangement to distribute stress, as illustrated in FIG. 18, by forming triangular external terminal electrodes 17 and 18 on a principal surface 16 of a ceramic element body 15 included in a ceramic electronic component 14, the principal surface 16 being positioned to direct the mounting surface side.
However, the electrode shape described in Japanese Unexamined Patent Application Publication No. 2001-126950 has the following problems.
Because areas of the external terminal electrodes 17 and 18 on the principal surface 16 arranged to direct the mounting surface side are reduced, fixation forces for holding the external terminal electrodes 17 and 18 fixed to the ceramic element body 15 are reduced in proportion.
Because areas of the external terminal electrodes 17 and 18 on the principal surface 16 positioned to direct the mounting surface side are reduced, contact areas of the external terminal electrodes 17 and 18 with a bonding material, such as a solder, are reduced in proportion. Accordingly, reliability in connection of the ceramic electronic component 14 with respect to the wiring board deteriorates.
As described in Japanese Unexamined Patent Application Publication No. 2003-309373, for example, it has recently been proposed to mount an electronic component in a state embedded in a wiring board. When such a technique is used, a via hole is formed by irradiating a laser beam to each of the external terminal electrodes of the electronic component from the wiring board side, and a conductor is filled into the interior of the via hole for connection to a circuit on the wiring board. In that case, if the areas of the external terminal electrodes 17 and 18 on the principal surface 16 arranged to direct the mounting surface side are relatively small as in the ceramic electronic component 14 illustrated in FIG. 18, a difficulty arises in accurately irradiating the laser beam so as to reach the external terminal electrodes 17 and 18.